Fuel cell system

Abstract

A fuel cell system is provided with a fuel cell stack assembly which includes a plurality of fuel cells which convert chemical energy from a fuel into electricity through a chemical reaction with an oxidizing agent, the plurality of fuel cells being stacked together in electrical series; a base member upon which the plurality of fuel cells are stacked such that the base member is in electrical communication with the plurality of fuel cells; an attachment member fixed to the base member, the attachment member being maintained at electrical ground; and a dielectric barrier which electrically isolates the base member from the attachment member.

We claim: 
     
         1 . A fuel cell system comprising:
 a fuel cell stack assembly comprising:
 a plurality of fuel cells which convert chemical energy from a fuel into electricity through a chemical reaction with an oxidizing agent, said plurality of fuel cells being stacked together in electrical series; 
 a base member upon which said plurality of fuel cells are stacked such that said base member is in electrical communication with said plurality of fuel cells; 
 an attachment member fixed to said base member, said attachment member being maintained at electrical ground; and 
 a dielectric barrier which electrically isolates said base member from said attachment member. 
   
     
     
         2 . A fuel cell system as in  claim 1  wherein said dielectric barrier comprises a dielectric member disposed between said base member and said attachment member such that said dielectric member spaces said base member from said attachment member. 
     
     
         3 . A fuel cell system as in  claim 2  further comprising a fastener which clamps said base member and said attachment member together in a clamping direction wherein said dielectric barrier further comprises an insulating washer which is clamped between said fastener and one of said base member and said attachment member in said clamping direction such that said insulating washer prevents said fastener from providing an electrically conductive path between said base member and said attachment member. 
     
     
         4 . A fuel cell system as in  claim 3  wherein said insulating washer is made of mica. 
     
     
         5 . A fuel cell system as in  claim 3  wherein said dielectric barrier further comprises an insulating sleeve which surrounds said fastener and is located between said fastener and said base member in a direction perpendicular to said clamping direction. 
     
     
         6 . A fuel cell system as in  claim 1  wherein said base member is a fuel cell manifold which includes a fuel cell manifold anode supply passage which supplies said fuel to a plurality of anodes of said plurality of fuel cells and which includes a fuel cell manifold anode exhaust passage which collects an anode exhaust from said plurality of fuel cells. 
     
     
         7 . A fuel cell system as in  claim 6  wherein said dielectric barrier comprises a dielectric member disposed between said fuel cell manifold and said attachment member such that said dielectric member spaces said fuel cell manifold from said attachment member. 
     
     
         8 . A fuel cell system as in  claim 7  wherein:
 said fuel cell stack assembly is one of a plurality of fuel cell stack assemblies such that said plurality of fuel cell stack assemblies are connected together in electrical series; and 
 said attachment member is a system manifold having a system manifold anode supply passage which is in fluid communication with said fuel cell manifold anode supply passage of each one of said plurality of fuel cell stack assemblies, said system manifold also having a system manifold anode exhaust passage in fluid communication with said fuel cell manifold anode exhaust passage of each one of said plurality of fuel cell stack assemblies. 
 
     
     
         9 . A fuel cell system as in  claim 8  wherein said dielectric member includes a dielectric passage therethrough which provides fluid communication between said system manifold anode supply passage and said fuel cell manifold anode supply passage or between said system manifold anode exhaust passage and said fuel cell manifold anode exhaust passage. 
     
     
         10 . A fuel cell system as in  claim 9  further comprising a seal within said dielectric passage which provides a gas-tight seal between said fuel cell manifold and said system manifold. 
     
     
         11 . A fuel cell system as in  claim 10  wherein said seal is held in compression between said fuel cell manifold and said system manifold and is electrically insulative. 
     
     
         12 . A fuel cell system as in  claim 8  wherein each one of said plurality of fuel cell stack assemblies further comprises a fastener which clamps said fuel cell manifold to said system manifold in a clamping direction wherein said dielectric barrier further comprises an insulating washer which is clamped between said fastener and one of said fuel cell manifold in said clamping direction and said system manifold such that said insulating washer prevents said fastener from providing an electrically conductive path between said fuel cell manifold and said system manifold. 
     
     
         13 . A fuel cell system as in  claim 12  wherein said insulating washer is made of mica. 
     
     
         14 . A fuel cell system as in  claim 12  wherein said dielectric barrier further comprises an insulating sleeve which surrounds said fastener and is located between said fastener and said fuel cell manifold in a direction perpendicular to said clamping direction. 
     
     
         15 . A fuel cell system as in  claim 8  wherein:
 said dielectric member is a first dielectric member; and 
 said dielectric barrier further comprise a second dielectric member disposed between said fuel cell manifold of one of said plurality of fuel cell stack assemblies and said fuel cell manifold of another one of said plurality of fuel cell stack assemblies such that said dielectric barrier electrically insulates said fuel cell manifold of said one of said plurality of fuel cell stack assemblies from said fuel cell manifold of said another one of said plurality of fuel cell stack assemblies. 
 
     
     
         16 . A fuel cell system as in  claim 6  wherein said fuel cell manifold also includes a fuel cell manifold cathode supply passage which supplies said oxidizing agent to a plurality of cathodes of said plurality of fuel cells and which includes a fuel cell manifold cathode exhaust passage which collects a cathode exhaust from said plurality of fuel cells. 
     
     
         17 . A fuel cell system as in  claim 16  wherein said dielectric barrier comprises a dielectric member disposed between said fuel cell manifold and said attachment member such that said dielectric member spaces said fuel cell manifold from said attachment member. 
     
     
         18 . A fuel cell system as in  claim 17  wherein:
 said fuel cell stack assembly is one of a plurality of fuel cell stack assemblies such that said plurality of fuel cell stack assemblies are connected together in electrical series; and 
 said attachment member is a system manifold having a system manifold anode supply passage which is in fluid communication with said fuel cell manifold anode supply passage of each one of said plurality of fuel cell stack assemblies, a system manifold anode exhaust passage in fluid communication with said fuel cell manifold anode exhaust passage of each one of said plurality of fuel cell stack assemblies, a system manifold cathode supply passage which is in fluid communication with said fuel cell manifold cathode supply passage of each one of said plurality of fuel cell stack assemblies, and a system manifold cathode exhaust passage which is in fluid communication with said fuel cell manifold cathode exhaust passage of each one of said plurality of fuel cell stack assemblies. 
 
     
     
         19 . A fuel cell system as in  claim 18  wherein said dielectric member includes a dielectric passage therethrough which provides fluid communication between said system manifold anode supply passage and said fuel cell manifold anode supply passage, between said system manifold anode exhaust passage and said fuel cell manifold anode exhaust passage, between said system manifold cathode supply passage and said fuel cell manifold cathode supply passage, or between said system manifold cathode exhaust passage and said fuel cell manifold cathode exhaust passage. 
     
     
         20 . A fuel cell system as in  claim 19  further comprising a seal within said dielectric passage which provides a gas-tight seal between said fuel cell manifold and said system manifold. 
     
     
         21 . A fuel cell system as in  claim 20  wherein said seal is held in compression between said fuel cell manifold and said system manifold and is electrically insulative. 
     
     
         22 . A fuel cell system as in  claim 18  wherein each one of said plurality of fuel cell stack assemblies further comprises a fastener which clamps said fuel cell manifold to said system manifold in a clamping direction wherein said dielectric barrier further comprises an insulating washer which is clamped between said fastener and one of said fuel cell manifold and said system manifold in said clamping direction such that said insulating washer prevents said fastener from providing an electrically conductive path between said fuel cell manifold and said system manifold. 
     
     
         23 . A fuel cell system as in  claim 22  wherein said insulating washer is made of mica. 
     
     
         24 . A fuel cell system as in  claim 22  wherein said dielectric barrier further comprises an insulating sleeve which surrounds said fastener and is located between said fastener and said fuel cell manifold in a direction perpendicular to said clamping direction. 
     
     
         25 . A fuel cell system as in  claim 18  wherein:
 said dielectric member is a first dielectric member; and 
 said dielectric barrier further comprise a second dielectric member disposed between said fuel cell manifold of one of said plurality of fuel cell stack assemblies and said fuel cell manifold of another one of said plurality of fuel cell stack assemblies such that said dielectric barrier electrically insulates said fuel cell manifold of said one of said plurality of fuel cell stack assemblies from said fuel cell manifold of said another one of said plurality of fuel cell stack assemblies. 
 
     
     
         26 . A fuel cell system as in  claim 1  wherein said plurality of fuel cells are held in compression by said base member and an end cap.